This invention relates to an internal locking mechanism for telescoping tubular members which utilizes friction to lock one telescoping member to another and method of making the same.
Heretofore, internal locking mechanisms that have been employed with telescoping members have required a cam surface mounted on a separate element or mandrel that is secured to the end of the inner telescoping member, so that as the pole is rotated the cam will bear against the outer telescoping member such as illustrated in U.S. Pat. No. 3,515,418. This requires two or more parts to construct in addition to the tubular telescoping members and the securing or fastening the separate parts into the inner tube member. Hence this device is weak due to the securement of one piece to another. In other words the twisting action can break the connection. Further, in applications where fluids will pass through the tubular members, the point of securement of the separate elements requires a seal to prevent leakage at this point.
In addition to that, there are various other types of friction engagement locking means which utilize mandrels or plugs which are inserted and secured within one end preferably the smaller of a telescoping member which then slides into the larger telescoping member where appropriate fittings are utilized so that by the twisting of one telescoping member against the other the offsets or cams will engage the surface and lock the member in place. These devices can be found in U.S. Pat. Nos. 3,667,788; 3,596,946; 2,873,129; 2,473,531.
Such plugs or mandrel type of locking devices have structural disadvantages over the present invention. Inherently, the friction type of locking members have utilized a minimal of three working parts namely the mandrel or plug with its formed surface which is fitted to the end of the inner tube, a locking ring of some type mounted on the mandrel, both of which are either cammed or stepped and the insertion of the mandrel in an outer telescoping tube. This has many disadvantages in that the cost of producing the locking device is uneconomical since it has required the separate mandrel to be formed first and then it must be inserted and secured by some means within the telescoping member. In the case where fluids are to be transmitted through the telescoping tubes, a seal is required where the mandrel is fitted into the end of the inner tube.
In addition, the previous prior art, in some cases, has utilized plastic mandrels and rings which have had a tendency to weaken when torque is applied to the members to effect the necessary tension. Finally, when the mandrel has been secured within the tube by whatever means such as wedging etc., there is always the possibility that a twisting of one telescoping member against another to lock the telescoping members in place, will cause the loosening of the mandrel and therefore, the locking device will be defeated because the mandrel will rotate freely within the smaller telescoping member.
Further, with the mandrel or plug type of friction of locking means as found in the prior art, the mandrel or plug has been solid in construction or at least only having a very small aperture extending there through. This has precluded the use of telescoping members with internal frictional locking means for a conduit of fluids. Where the mandrel did have an axial bore or opening extending therethrough to allow fluids to enter, the mandrel would require considerable sealing in order to prevent fluid from seeping out between the tube and the locking mechanism.
In addition to the above cited patents, applicant is aware of the following U.S. Pat. Nos. 3,095,825; 3,044,410; 2,517,700; 2,494,878; and 3,953,138. None of these disclose the present invention.